1. Field of the Invention
This invention relates to valve actuators, and is more particularly concerned with fail-safe valve actuators in which a torsion spring is wound during operation of the valve in a first direction to store energy for returning the valve in the opposite direction upon disconnection of power from the actuator, such disconnection being either intentional or by way of power failure or the like.
2. Description of the Prior Art
In my U.S. Pat. No. 3,808,895, issued May 7, 1974, I disclose an electric fail-safe valve actuator of the type generally mentioned above. The actuator comprises an electric motor which is coupled to an output shaft by way of a gear train and an intermediate shaft. The intermediate shaft and the output shaft are axially aligned and have adjacent ends embraced by a torsion spring which enages or releases the two shafts, with respect to mutual rotation, through the energization and deenergization of a solenoid which encircles the output shaft and which has an annular cup-shaped operating member which moves axially along the shaft to engage and disengage the torsion spring. A second torsion spring has one end connected to the housing of the actuator and the other end connected to the output shaft so as to be wound to store energy during driving of the output shaft in a first direction. A brake mechanism connected to the motor holds the valve in its operated condition until such time as power is deliberately or accidentally removed from the circuit, whereupon the torsion spring clutch mechanism disengages the intermediate and output shafts and the second torsion spring, acting as a motor, releases its energy to drive the valve in the opposite direction. A pin connected to the output shaft and traveling in an arcuate slot in a fixed plate strikes a bumper at the end of the slot as a stop and limit defining structure.